This invention relates generally to a device or microdevice, and to disposition of structural components of the same. More particularly, the invention is concerned with a device and disposition of structural components of the same which is to be produced through a multiple exposure process wherein different types of patterns are printed superposedly by a first exposure process as can be represented by a standard or ordinary exposure process such as a projection exposure process, and a second exposure process of a higher resolution than the first exposure process, whereby a pattern (hereinafter, xe2x80x9cdesired pattern to be producedxe2x80x9d) having a smallest linewidth corresponding to the second exposure process can be produced. The present invention can be applied suitably to various devices such as, for example, a semiconductor chip (IC or LSI, for example), a display device (liquid crystal panel, for example), a detecting device (magnetic head, for example) and an image pickup device (CCD, for example).
Currently, many projection exposure apparatuses for manufacture of devices such as ICs, LSIs or liquid crystal panels, for example, based on photolithography, use a light source of an excimer laser. However, simply using such excimer laser as a light source in a projection exposure apparatus does not assure formation of a fine pattern having a linewidth of 0.15 micron or less.
In order to improve the resolution, it is necessary to enlarge the numerical aperture (NA) of a projection optical system or to shorten the wavelength of exposure light. Practically, however, it is not very easy to enlarge the NA or shorten the exposure wavelength. This is because: since the depth of focus of a projection optical system is inversely proportional to the square of the NA while it is proportional to the wavelength xcex, enlargement of the NA of the projection optical system causes a decrease of the depth of focus, thus making more difficult to accomplish the focusing and thus slowing down the productivity. Further, most glass materials have an extraordinarily low transmission factor with respect to a deep ultraviolet region. Even for a fused silica (quartz) which is, used with a wavelength xcex=248 nm (KrF excimer laser), the transmission factor reduces almost to zero when used with a wavelength xcex=193 nm or less. Currently, no glass material has been developed that can be practically used in a region of exposure wavelength xcex=150 nm or less, corresponding to a fine pattern of 0.15 micron linewidth or less to be produced in accordance with a standard or ordinary exposure process.
Japanese Patent Application, Application No. 304232/1997, (hereinafter, xe2x80x9cthe earlier Japanese patent applicationxe2x80x9d), filed by the assignee of the subject application, proposes a dual exposure process which is based on a combination of dual-beam interference exposure and standard exposure, wherein a multiple-value exposure amount distribution is applied to a substrate, to be exposed, to assure high resolution exposure. In an embodiment disclosed in the earlier Japanese patent application, the dual-beam interference exposure process is performed by use of a phase shift mask having a line-and-space (LandS) pattern of 0.1 micron linewidth, and a fine-line pattern is printed through coherent illumination. Thereafter, an ordinary exposure process (for example, an exposure process based on partially coherent illumination) is performed while using a mask which is formed with a pattern having portions of different transmission factors and having a shape corresponding to an actual device pattern of smallest linewidth of 0.1 micron. In accordance with the method disclosed in the earlier Japanese patent application, a pattern of smallest linewidth of 0.10 micron may be formed through the ordinary exposure process and by using a projection exposure apparatus having a projection optical system which has an image side NA of 0.6.
Another method for the fine pattern printing is a probe exposure method wherein a pattern is drawn and printed on a photosensitive member by using a probe. The probe may be based on AFM using an inter-atomic force, STM using a tunnel current, an electron beam, a laser beam or proximity light, for example. However, performing the probe exposure over the whole exposure area has a disadvantage of low throughput. In consideration of it, those portions of a desired pattern to be produced that can be produced through an ordinary exposure process may be photoprinted by using a light quantity larger than an exposure threshold of a photosensitive substrate. On the other hand, those portions of insufficient resolution may be photoprinted by superposed printing which is based on an ordinary exposure and a probe exposure, with the respective light quantities each being lower than the exposure threshold of the photosensitive material but both, when combined, being higher than the exposure threshold. As a result, a multiple-value exposure amount distribution similar to that described above is applied (Japanese Patent Application, Application No. 137476/1998).
In the multiple exposure process described above (hereinafter, xe2x80x9cIDEAL exposure processxe2x80x9d), when a Levenson mask is used, a fine line pattern is formed only in a region where Levenson mask data is present. Thus, the disposition of the pattern is restricted by the pitch of the Levenson mask (i.e., the linewidth and the spacing).
It is an object of the present invention to provide optimum disposition of structural components of a device when the device is to be manufactured on the basis of the xe2x80x9cIDEAL exposure processxe2x80x9d.
Specifically, it is an object of the present invention to provide an optimum solution for disposition of structural components of a device, such as a contact, a semiconductor region and a gate of the device, for example, to attain largest improvements in integration density or device performance, during the semiconductor manufacturing processes where a number of exposure processes are repeated.
It is another object of the present invention to provide a microdevice having structural components disposed in accordance with the best solution above.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.